The present invention relates to passive optical networks, and in particular to a method and apparatus for providing flexibility in the protection afforded by such networks.
Passive optical networks (PON) are known to be effective for distributing broadband and cable TV services directly to customers using optical fibre. Current passive optical network systems can offer full protection down to the customer but require complete duplication of (a) the fibre feeder from the exchange, (b) the splitter/combiners, (c) the customer drops, and (d) the electro-optical transceivers.
PON feeder protection alone requires duplication of every fibre down to every drop splitter. This doubles the fibre feeder requirements, with consequent potential duct congestion and excessive costs, and is especially expensive for long thin routes where duct space is also generally scarce.
There is at present therefore a strong demand from network operators to reduce the costs of fibre deployment to smaller customer sites (e.g. small businesses) and to the home. Equally, the standards for a are becoming more concerned with PON protection, as are many telecommunications manufacturers.
SDH/SONET rings are good for supporting larger businesses, but become expensive when only a few E1/T1""s are required, especially if the locations of the subscribers"" drop points are scattered. To date, operators have accepted that SDH/SONET solutions are needed for larger customers, but as the market migrates towards smaller businesses and residential customers, cost pressures dictate that more pragmatic, lower cost PON-type solutions are required. This has so far not happened since PON systems could not provide the high levels of availability required at competitive prices. It is therefore important to find a solution to the provision of cheaper alternatives to the existing SDH/SONET networks, whilst providing the same protection flexibility, in order to satisfy the commercial demand.
The invention seeks to provide an improved method and apparatus for providing protection in passive optical networks.
According to a first aspect of the present invention there is provided an optical splitter/combiner arrangement for a passive optical network comprising two through optical ports and at least one drop optical port, and wherein a first optical path is provided between said through ports and a second optical path is provided between one of said through ports and one of said drop optical ports.
In one preferred embodiment, losses associated with said first optical path are lower than losses associated with said second optical path.
In a further preferred embodiment, a relatively high loss path is provided between one of said through ports and each of said drop ports.
In a further preferred embodiment, wherein a relatively high loss path is provided between each of said through ports and one of said drop ports.
In a further preferred embodiment, wherein a relatively high loss path is provided between each of said through ports and each of said drop ports.
In a further preferred embodiment, arranged to split signals received on one of said drop ports between each of said through ports.
In a further preferred embodiment, the optical splitter/combiner arrangement comprises first and second asymmetrical splitter/combiners optically connected to each other to form a low loss optical path and each optically connected to a common one of said through ports, and each optically connected to a third splitter/combiner optically connected to said at least one drop port.
In a further preferred embodiment, the optical splitter/combiner arrangement comprises an asymmetrical splitter/combiner optically connected to each of said through ports and providing a low loss path between said ports, and each optically connected to a third splitter/combiner optically connected to said at least one drop ports to form a relatively higher loss path between said through ports and said drop ports.
In a further preferred embodiment, the optical splitter/combiner comprises only one optical splitter/combiner.
In a further preferred embodiment, the optical splitter/combiner arrangement comprises a WDM splitter/combiner.
According to a further aspect of the present invention there is provided a passive optical network comprising a splitter/combiner arrangement according to the first aspect.
In one preferred embodiment, each of said two through ports of said splitter/combiner arrangement is optically connected via a linear optical network to a distinct OLT transceiver.
In a further preferred embodiment, said splitter/combiner arrangement is arranged to convey signals between each of said distinct OLT transceivers and said at least one drop ports whereby to provide protection against single point failure in said linear network.
In a further preferred embodiment, said distinct OLT transceivers are physically separated whereby to provide dual homing.
Advantageously, the passive optical network may comprise a plurality of splitter/combiner arrangements wherein said splitter/combiner arrangements are configured to provide a plurality of distinct degrees of protection against faults in the network.
The invention also provides a passive optical network comprising a plurality of splitter/combiner arrangements according to the first aspect wherein said splitter/combiner arrangements are configured to provide a plurality of distinct degrees of protection against faults in the network.
There is also provided a passive optical network comprising: a plurality of optical splitters/combiners each comprising first and second through ports and at least one drop port; wherein said through ports of said plurality of splitters/combiners are concatenated to form a linear arrangement having two end through ports; whereby optical signals may be transmitted between said end through ports by means of said linear arrangement; and wherein signals may be transmitted between at least one of said end through ports and one of said drop ports by means of said linear arrangement.
There is also provided an optical splitter/combiner arrangement comprising: first, second and third optical ports; and at least one drop optical port; and wherein a relatively low loss path is provided between said first and second ports, a relatively high loss path is provided between said first optical port and said at least one drop optical ports, and a relatively high loss path is provided between said third optical port and said at least one drop optical port.
In one preferred embodiment, it additionally comprises: a fourth optical port; and wherein a relatively high loss path is provided between said second and fourth optical ports and a relatively high loss path is provided between said fourth port and said at least one drop optical ports.
Th invention also relates to a passive optical network comprising such a splitter/combiner arrangement.
In a further preferred embodiment, each of said first optical port of said splitter/combiner arrangement is connected via a linear optical network to a first OLT transceiver, and said second and third optical ports of said splitter/combiner arrangement are each optically connected via a linear optical network to a second OLT transceiver.
In a further preferred embodiment, said splitter/combiner arrangement is arranged to convey signals between each of said first and second OLT transceivers and said at least one drop port whereby to provide protection against single point failure in said linear optical networks.
The invention also provides for a system for the purposes of digital signal processing which comprises one or more instances of apparatus embodying the present invention, together with other additional apparatus.
The invention is also directed to a method by which the described apparatus operates and including method steps for carrying out every function of the apparatus.
According to a further aspect of the present invention there is provided a method of adding a drop point to a PON comprising at least one drop point optically connected by a linear arrangement of fibre lines to first and second OLT transceivers, comprising the steps of: severing one of said fibre lines to expose two fibre ends; providing a drop point arrangement according to the first aspect; coupling said exposed fibre ends to said drop point arrangement.
In one preferred embodiment, the method is performed while the PON is carrying traffic.
According to a further aspect of the present invention there is provided a method of upgrading a PON comprising a plurality of drop points optically connected by a linear arrangement of fibre lines to first and second OLT transceivers, comprising the steps of: severing one of said fibre lines to expose two fibre ends; providing third and fourth OLT transceivers; providing optical fibre lines; coupling said exposed fibre ends via said optical fibre lines to said third and fourth OLT transceivers.
In one preferred embodiment, the method is performed while the PON is carrying traffic.
According to a further aspect of the present invention there is provided a method of providing a PON comprising: providing a pair of transceivers, providing a plurality of optical fibre lengths; providing at least one splitter/combiner drop point arrangement; connecting said fibre lengths and said splitter/combiner drop point arrangement to form a linear network connecting said at least one splitter/combiner drop point arrangement and connecting said transceivers to opposite ends of said linear network; and wherein one transmitter and one receiver of said pair of transceivers operates in main mode and another transmitter and another receiver of said pair of transceivers operates in warm standby mode; and arranged to provide single point failure protection in the network between said transceivers.
The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.